1. Technical Field
The present invention relates to a resonator element, a resonator, an oscillator, an electronic device, and a moving object.
2. Related Art
A so-called two-legged tuning fork type quartz crystal resonator is known as a resonator (for example, refer to JP-A-2004-266871). For example, as disclosed in JP-A-2004-266871, a resonator element included in the resonator includes a base portion and two vibrating arms extending from the base portion so as to be parallel to each other, and fluxurally vibrates the two vibrating arms in an in-plane direction so that the arms alternately repeat mutual approach and separation.
A pair of grooves are formed, along a longitudinal direction, in each vibrating arm of the resonator element according to JP-A-2004-266871 so that a cross-section of each vibrating arm has a substantially H shape. Further, as disclosed, in JP-A-2004-266871, it is possible to reduce so-called vibration leakage in which vibrations of the vibrating arms leak to the base portion side, by providing a notch in the base portion. Here, from dimensions of parts disclosed in JP-A-2004-266871, a Q value of the resonator element is 31,573 as shown in the following table.
TABLE 1PlateGrooveBankArmthicknessDepthportionwidth[μm][μm]width [μm][μm]ηQ valueJP-A-2004-10043151000.30031,573266871
Meanwhile, when a width of an arm portion of the vibrating arm is set to W1 and a width of each of principal surfaces (hereinafter, referred to as banks) which are positioned on both sides of the groove, when seen in a plan view, is set to W3, η can be expressed by the relation of η=2×W3/W1. So-called η is an occupancy rate of a width of the bank with respect to the width of the arm portion.
However, in recent years, the need for a further improvement in a Q value has increased. Consequently, in a resonator element according to JP-A-2011-199331, as means for improving a Q value, a vibrating arm includes a first arm portion (arm portion) and a second arm portion (weight portion) which is provided at a distal end of the first arm portion and has a width larger than that of the first arm portion. Thus, it is possible to increase a Q value.
Further, as disclosed in JP-A-2011-199331, in the resonator element, an occupancy rate of a length of a weight portion with respect to a length of the vibrating arm is set to equal to or greater than 30% and a ratio of a width of the weight portion (second arm portion) to a width of an arm (first arm portion) is set to equal to or greater than 2, and thus it is possible to prevent a vibration of a second harmonic and to reduce crystal impedance (CI value, equivalent series resistance). However, when the length of the vibrating arm is made constant and a resonance frequency of a fundamental wave is set to, for example, 32.768 (kHz), in a case where the vibrating arm is merely configured to include the first arm portion and the second arm portion (weight portion), the frequency may be reduced from 32.768 (kHz) due to a weight effect of the weight portion. Accordingly, it is necessary to increase the width of the first arm portion of the vibrating arm in order to maintain a constant resonance frequency, for the purpose of avoiding the reduction in the frequency. Meanwhile, there is a concern that stress may concentrate on a bonding portion between the first arm portion and the second arm portion (weight portion). Thus, it is necessary to optimize a relationship between the width of the first arm portion and the width of the second arm portion (weight portion) so that damage does not occur in a case where excessive external force is applied thereto, and to improve impact resistance while maintaining the frequency of 32.768 (kHz).
JP-A-2011-019159 is an example of the related art.